Excavation is a necessary part of the repair procedure for many types of services which run under roadways, parking lots and other finished surfaces, for example a gas or water line running underneath a road or sidewalk. Traditionally, a jackhammer or trimack are used to break up the concrete or asphalt and an excavating machine such as a backhoe would remove the surface cover and uncover the service requiring maintenance and repair. The repair or other servicing would be effected, the excavation backfilled, and the surface refinished using a comparable material (asphalt, concrete, etc. as required to blend in with the surrounding surface finish).
This type of excavation is costly, in terms of both the inconvenience which results from having to remove and refinish a large portion of the road, sidewalk or other finished surface, particularly for example on a busy roadway, and the size of the hole which must be repaired following servicing. Many repair and maintenance procedures do not require a large excavation, and very localized access is sufficient to enable work crews to affect the service procedure. However, conventional excavating machinery is incapable of excavating with the precision required to provide only the opening necessary to access the service being repaired.
Accordingly, an excavating system comprising a rotary cutter mounted on a truck has been developed for performing what is commonly known as a “keyhole” excavation. The cutter is effectively a large hole saw, which cuts a circular “coupon” or “core” out of the finished surface allowing localized access to the service requiring maintenance or repair, mounted to a motor which is in turn mounted on a large drill press.
In such a keyhole excavation device the rotary cutting tool is mounted on a turret so that it can be positioned at various angles about the truck. A hydraulic actuator operates the press, forcing the rotating cutting head into the finished surface at a controlled rate to cut the core. Once the cutting head has penetrated the surface it is retracted to remove the core, and the core is placed aside. The opening is excavated down to the depth of the pipe in need of servicing using conventional vacuum technology, the repair or other service procedure effected, and the opening is backfilled. The core is then placed on a bed of bonding agent to refinish the surface. When the bonding agent hardens, the core has been reintegrated with the surface and in all cases the separation of the core from the surrounding surface will be barely noticeable. The savings of time and avoidance of inconvenience by effecting repairs and servicing through such keyhole excavation, and especially the savings in restoration costs, is significant.
The keyhole excavation is often required beside a roadway which may not be fully accessible to the truck, so the rotary cutter head is mounted on an arm which can move about the truck on a turret within an arc of approximately 270°. This allows the cutting head to be positioned along either side of the truck, or along the back of the truck, which permits some flexibility in the positioning of the truck, to ensure that the truck is in a stable position before cutting commences. For example, the truck can be positioned on the shoulder of a road, or within one lane, so as to minimize the disruption of vehicular traffic.
However, the vertical hydraulic press assembly used to force the cutting head into the finished surface is supported on a horizontal arm which has a single stabilizing point, i.e. at the turret, and it is accordingly difficult to keep the press—and thus the cutter—stable during drilling. Imperfections in the cutting head and obstructions in the finished surface cause the support arm to vibrate. These vibrations are transferred to the vertical press, which causes the support arm to shift about the drilling access which in turn causes the vibration to increase. The resulting instability makes cutting difficult in some cases, and limits the size and depth of the rotary cutter head because a deeper rotary cutter head both causes greater vibration and, due to the greater distance between the cutting edge and the shaft, shifts more under the influence of the vibration.
It would accordingly be advantageous to provide a more stable system and method for cutting a core out of a finished surface as part of a keyhole excavation process.